The present invention relates to a fluid friction clutch. More particularly, the present invention relates to a fluid friction clutch having a housing filled with a viscous fluid, a shaft projecting into the housing, interengaging plates non-rotatably connected to the housing and the shaft, and spacers disposed in the gaps between the plates. The plates are displaceable in the axial direction so that the magnitude of the gaps between the plates can be varied.
In fluid friction clutches of this type, torque is transmitted by the shearing stresses which arise in the viscous fluid contained within the gaps between the interengaging plates. The magnitude of these shearing stresses depends upon the viscosity of the fluid and the velocity gradient between the two sets of plates. One of the problems associated with such fluid friction clutches is the lowering of the viscosity of the fluid, and consequently the drop in transmittable torque, when the temperature of the viscous fluid rises. Such increases in the temperature of the viscous fluid may arise from slippage in the clutch or from an external heat source.
The drop in transmittable torque can be compensated for by increasing the velocity gradient, i.e., by increasing the difference in rotational speeds between the driving and the driven coupling parts. Alternatively, the decrease in transmittable torque can be compensated for by decreasing the size of the spacings or gaps between the plates.
In many cases, it is not possible, or at least not desirable, to increase the differential speed between the driving and the driven parts of the clutch units. Therefore, in order to compensate for the loss in transmittable torque, it is desirable to adjust the magnitude of the gaps between the plates when the temperature of the viscous fluid changes.
A number of fluid friction clutches are already known in which the spacings between the plates can be varied. For example, in U.S. Pat. No. 1,238,447 (Severy), a friction clutch is described having a plurality of coaxial ring lugs which serve as the mutually interengaging coupling members. These ring lugs are conically shaped. Each set of ring lugs is aligned with and offset from the gaps between the ring lugs of the other set. The ring lugs are caused to interengage when the disks to which they are attached are displaced. Due to the conical shape of the inner and outer peripheral surfaces of the ring lugs, a different gap width results between the ring lugs, the gap width depending upon the depth of penetration of the ring lugs. Thus, it is possible to vary the magnitude of the transferrable torque in the clutch disclosed in this patent by varying the magnitude of the gaps between the ring lugs which function as the coupling members. However, this patent does not disclose varying the gaps between the ring lugs in accordance with temperature variations in the viscous fluid.
In British Pat. No. 1,412,583 (Rolt et al.), a fluid friction clutch of a different kind is described. In the fluid friction clutch of this patent, gaps are provided between interengaging inner and outer plates and spacers are disposed within these gaps. However, the spacers disclosed in this patent are simple wire rings. No provision is made in this patent for adjusting the gap width between the plates.
It is therefore an object of the present invention, to provide a fluid friction clutch having mutually interengaging plates wherein the size of the gaps between the plates is independently and automatically regulated in accordance with the temperature in the clutch unit. In this manner, any reduction in transmittable torque due to an increase in the temperature of the viscous fluid will be compensated for.